Empirical model for the autotrophic biodegradation of thiocyanate in an activated sludge reactor

Aims: The aim of this investigation was to develop an empirical model for t he autotrophic biodegradation of thiocyanate using an activated sludge reac tor. Methods and Results: The methods used for this purpose included the use of a laboratory scale activated sludge reactor unit using thiocyante feed conc entrations from 200 to 550 mg 1(-1) Reactor effluent concentrations of <1 m g 1(-1) thiocyanate were consistently achieved for the entire duration of t he investigation at a hydraulic retention time of 8 h, solids (biomass) ret ention of 18 h and biomass (dry weight) concentrations ranging from 2 to 4 g 1(-1). A biomass specific degradation rate factor was used to relate thio cyanate degradation in the reactor to the prevailing biomass and thiocyanat e feed concentrations. A maximum biomass specific degradation rate of 16 mg (-1) g(-1) h(-1) (mg thiocyanate consumed per gram biomass per hour) was ac hieved at a thiocyanate feed concentration of 550 mg 1(-1). The overall yie ld coefficient was found to be 0.086 (biomass dry weight produced per mass of thiocyanate consumed). Conclusions: Using the results generated by this investigation, an empirica l model was developed, based on thiocyanate feed concentration and reactor biomass concentration, to calculate the required absolute hydraulic retenti on time at which a single-stage continuously stirred tank activated sludge reactor could be operated in order to achieve an effluent concentration of <1 mg 1(-1). The use of an empirical model rather than a mechanistic-based kinetic model was proposed due to the low prevailing thiocyanate concentrat ions in the reactor. Significance and Impact of the Study: These results represent the first emp irical model, based on a comprehensive data set, that could be used for the design of thiocyanate-degrading activated sludge systems.